What was it that Wally and Beaver used to say? It was the equivalent of "cool" today but I can't remember. Any ideas?

Probably the closest term for the same idea was "neat," as used in "It's real neat," or "Are you saying I'm not a neat guy?"

They used "swell" alot too that was also kind of like another word for cool.

Another word that I seem to remember being used a lot was the term "keen". As in, "That's real keen, dad." It's another word equivalent to cool. :)